There exists a need for a highly flexible, non-porous tubing for various, primarily medical applications. These applications typically involve the insertion of the tubing into a living body, either temporarily or as a permanent implant. Temporary applications include the use of the tubing as a catheter tubing to convey fluids into or out of a body, or alternatively as the tubing portion of a medical device such as an endoscope. Present endoscope channel tubes are made of porous expanded PTFE having a microstructure of nodes interconnected by fibrils, made as taught by U.S. Pat. Nos. 4,187,390 and 3,953,566. These tubes typically have a very small pore size with a fibril length of less than five microns. They are quite flexible, inert, biocompatible and lubricious. However, due to the porosity of the tubing, during use various contaminants such as proteins and calcium tend to penetrate the void spaces present on the inner surface of the tube and to adhere to the inner surface. The adhesion of contaminants to the inner surface of the tube resulted in a decline in the slip properties of the inner surface, and also impaired other tube functions such as its flexing properties. Moreover, washing and sterilization were necessary in order to remove the contaminants so that the tube could be reused. Washing and sterilization were time consuming, and represented a burdensome operation.
Various methods of improving this porous PTFE tube have been attempted. For example, a tube in which an elastomer coating has been formed on the inner surface of the tube has been proposed (Japanese Laid-Open Patent Applications 54-74514, 59-25725). However, while a tube furnished with such an inner surface elastomer coating has improved resistance to contamination, the continuous elastomer coating, which has slip properties inferior to those of PTFE, constitutes the inner surface of said tube, and as a result the slip properties of the inner surface are diminished. Moreover, large numbers of wrinkles are produced in the coating during flexing, resulting in a further loss of slip properties.
In Japanese Patent Publication 61-47547, a porous PTFE tube wherein portions of said tube were impregnated with a solution of a vinylidene fluoride/tetrafluoroethylene copolymer, polyvinyl chloride, or another synthetic resin lacking elastic force, and then heated and dried so that portions of the tube were filled with the synthetic resin and rendered rigid thereby is disclosed. The mechanical strength of the tube was increased by rendering portions of it rigid, but the overall flexibility of the tube was significantly diminished; moreover, since the resin was contained in only a portion of the inner surface of the tube, the resistance of the inner surface to contamination was not improved.
In Japanese Laid-Open Patent Application 2-147065, a tube for medical use wherein the surface of a porous resin tube was coated with a solution of a synthetic resin such as polyvinyl chloride, dried, and a water soluble polymer coating formed on the resin surface was proposed. However, since this tube contained a synthetic resin which possessed no elastic force, the overall flexibility of the tube was insufficient; moreover, the synthetic resin was merely applied to the tube surface in the form of a solution and then dried so that formation of a continuous thin coat of said resin was unavoidable, with the result that the slip properties of the surface were diminished.
A porous resin tube which contained a synthetic resin was also disclosed in Japanese Laid-Open Patent Application 55-82884. However, in the case of this tube as well, the synthetic resin was applied to the tube inner surface in the form of a solution, caused to impregnate the pores, and cured, with the result that a continuous coat of the synthetic resin necessarily formed on the inner surface, thus diminishing the slip properties of the inner surface. Moreover, since the resin contained in the tube was a thermoplastic resin, it lacked a crosslinked structure, and thus the resistance to chemicals was poor.